The present invention relates to a radiological imaging apparatus and a positron emission tomographic apparatus.
In the conventional radiological imaging apparatus, there has been an apparatus in which γ-rays emitted from an examinee who is a subject to be examined is detected by using a detector comprising a scintillator, a photomultiplier tube, and the like so that a tomographic of the subject is obtained (for example, JP-U-7-29489 (paragraphs [0007]-[0008], FIG. 1, FIG. 2)). This detector, for example, is constituted such that a large photomultiplier tube (referred to also as photomul) is placed behind a single crystal such as a sheet of big NaI and the like, and is formed in a single layer in the direction of the radiation of γ-rays, and 511 KeV or around that value which is an energy of γ-rays from the subject is detected. Consequently, no energy of low γ-rays is detected. Further, there has been disclosed a technology for solving a heating problem arising from power consumption of 250 W by a radiation detecting element in the radiological imaging apparatus (for example, JP-A-63-49140 (Page 2)).
Now, as the radiological imaging apparatus of recent years, particularly as the positron emission tomographic apparatus, a positron emission tomographic apparatus using a semiconductor radiation detector is considered so as to highly accurately detect a position of generating source of γ-rays in the examinee (for example, JP-A-2003-167058 (Page 2)). This positron emission tomographic apparatus disposes semiconductor radiation detectors of a plurality of layers in the direction orthogonal to the longitudinal direction of a bed. For example, γ-rays having passed through the semiconductor radiation detector inside the inner most layer are detected by the semiconductor radiation detector inside the layer located outside thereof. Further, one γ-ray from a pair of γ-rays emitted from the examinee is absorbed in a part (for example, 300 keV) of energy of 511 keV in the semiconductor radiation detector inside the inner most layer, and is scattered, and after that, the remaining energy (for example, 211 keV) is sometimes absorbed in the semiconductor radiation detector inside the layer located outside. One semiconductor radiation detector outputs a γ-ray detection signal of energy of 300 KeV, and the other semiconductor radiation detector outputs a γ-ray detection signal of energy of 211 KeV.
In case γ-rays are scattered by the semiconductor radiation detector, a γ-ray detection signal of low energy is outputted from a plurality of semiconductor radiation detectors. When such a γ-ray radiation detection signal of low energy, for example, a γ-ray detection signal of 211 keV is affected by noise, its γ-ray detection signal cannot be used.
An object of the present invention is to provide a radiological imaging apparatus and a positron emission tomographic apparatus capable of shortening an examination time.